Database management systems 3rd

Welcome to my “Database management systems 3rd .”

Main functions of the DBMS

    data management in external memory (on disks);

    data management in RAM using disk cache;

    logging changes, backing up and restoring the database after a failure;

    support for database languages (data definition language, data manipulation language).

Usually, the modern DBMS contains the following components:

    core, which is responsible for managing data in external and operative memory and logging,

    a database language processor that optimizes requests for retrieving and modifying data and creating, as a rule, a machine-independent executable internal code,

    a runtime support subsystem that interprets data manipulation programs that create a user interface with the DBMS

    as well as service programs (external utilities) that provide a number of additional options for servicing the information system.

The database representation is used in the form of a tree (hierarchical) structure, consisting of objects (data) of different levels.

Between the objects there are links, each object can include several objects of a lower level. Such objects are in relation to the ancestor (object closer to the root) to the descendant (the object of a lower level), and it is possible that the ancestor object has no descendants or has several of them, whereas the descendant object has only one ancestor. Objects that have a common ancestor are called twins (in the programming with respect to the data structure of the tree, the name of the brothers settled).

A hierarchical database is a file system consisting of a root directory in which there is a hierarchy of subdirectories and files.

Examples: Caché, Google App Engine Datastore API.

Network

Network databases are similar to hierarchical, except that they have pointers in both directions that connect related information.

Examples: Caché.

Relational

Almost all developers of modern applications that provide communication with database systems are oriented towards relational DBMSs. According to Gartner, in 2013 the market for relational DBMSs was $ 26 billion with an annual growth of about 9%, and by 2018 the relational database market will reach $ 40 billion. At present, Oracle, IBM, and Microsoft are absolute leaders in the database market with a total cumulative market share of about 90%, delivering systems such as Oracle Database, IBM DB2, and Microsoft SQL Server.

Object-oriented

Manage databases in which data is modeled as objects, their attributes, methods, and classes.

This kind of DBMS allows you to work with database objects in the same way as with objects in programming in object-oriented programming languages. OODBMS expands programming languages, transparently introducing long-term data, concurrency control, data recovery, associated queries and other capabilities.

Examples: GemStone.

Object-relational

This type of DBMS allows using the capabilities of the object-oriented approach through objects, classes, and inheritance through extended database structures and query language.

Often, all those databases, which are called relational, are, in fact, object-relational.

In this course we will, first of all, talk about this kind of DBMS.

Examples: PostgreSQL, DB2, Oracle, Microsoft SQL Server.

By degree of distribution

    Local DBMS (all parts of the local DBMS are located on the same computer)

    Distributed DBMS (DBMS parts can be hosted on two or more computers).

By the way of access to the database

File-server

In file-server DBMS, data files are located centrally on the file server. The DBMS is located on each client computer (workstation). DBMS access to data is carried out through a local network. Synchronization of reads and updates is performed through file locks. The advantage of this architecture is the low load on the file server processor. Disadvantages: the potentially high load of the local network; Difficulty or impossibility of centralized management; difficulty or inability to provide such important characteristics as high reliability, high availability and high security. They are used most often in local applications that use database management functions; in systems with low data processing intensity and low peak load on the database.

At the moment, file-server technology is considered obsolete, and its use in large information systems is a disadvantage.

Examples: Microsoft Access, Paradox, dBase, FoxPro, Visual FoxPro.

Client-server

The client-server DBMS is located on the server along with the database and accesses the database directly, in exclusive mode. All client requests for data processing are processed centrally by the client-server DBMS. The disadvantage of client-server DBMSs is the increased requirements for the server. Advantages: potentially lower LAN load; convenience of centralized management; the convenience of providing such important characteristics as high reliability, high availability and high security.

Examples: Oracle, Firebird, Interbase, IBM DB2, Informix, MS SQL Server, Sybase Adaptive Server Enterprise, PostgreSQL, MySQL, Caché, Linter.

Built-in

Embedded DBMS is a DBMS that can be supplied as part of a software product without requiring a self-installation procedure. An embedded DBMS is designed for local storage of its application data and is not designed for collective use on the network. The physically built DBMS is most often implemented as a plug-in library. Access to the data from the application side can occur via SQL or through special APIs.

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